Today’s cool image revisits Lycus Sulci, the largest mountain range on Mars, about 1,400 mile wide and 1,800 miles long. The overview map to the right gives a sense of the roughness and chaotic nature of this region, extending north from Mars’ largest volcano, Olympus Mons.

At present scientists are unsure of the geology that formed Lycus Sulci, and how it is linked with Olympus Mons. The wide view to the right suggests it is the remains of a very ancient lava flow descending from the volcano that over time has become eroded to produce this wildly knobby terrain. That hypothesis remains unproven however. There is also evidence that the material here might instead be volcanic ash, deposited in many layers and eroded away with time.

The location of the cool image below is marked by the white dot, with the inset providing us a wider view of the surrounding terrain. Note the two craters to the north and west. Both appear to have been partly filled by flows coming from the south and east, respectively, adding weight to the theory that this region formed from lava flow.

Click for original image.

The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on April 30, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The largest mesa in the picture is about 500 feet high.

Note the many slope streaks. Lycus Sulci is known for its slope streaks, and most MRO photos of this region seem focused on monitoring these features. In this case this is the first MRO high resolution picture of this particular spot, so it is presently difficult to know how these streaks have changed over time. The origin of these streaks is at present not understood.

Note also the many dunes in the low-lying hollows. This large quantity of dust, likely volcanic ash, suggests strongly that these terrain is layered ash, not lava. Or maybe it is a complex combination of both.

Orbital data cannot answer this question. We need to walk the surface to find out.